Various synthetic methods for making substituted hydroxylamines useful in photographic processing solutions are known, for example, in U.S. Pat. No. 3,287,125 (Green et al), U.S. Pat. No. 3,778,464 (Klemchuk), U.S. Pat. No. 4,876,174 (Ishikawa et al) and U.S. Pat. No. 5,354,646 (Kobayashi et al).
More specific synthetic methods for producing carboxyalkyl substituted hydroxylamines are described in U.S. Pat. No. 5,110,985 (Hayakawa et al). The preferred method involves reacting an .alpha.,.beta.-unsaturated carboxylic acid with a mono-substituted hydroxylamine in a variety of solvents, including water and mixtures of water and water-miscible solvents. The hydroxylamines are preferably used in the form of hydrochlorides or sulfates that must be neutralized with a base (such as sodium hydroxide, sodium carbonate or pyridine). The resulting substituted hydroxylamine product is isolated from the reaction mixture prior to use. Undesirable by-products also are produced, this being another reason for isolation of the desired hydroxylamine product prior to use.
Related U.S. Pat. No. 5,248,811 (Morimoto et al) and U.S. Pat. No. 5,262,563 (Morimoto et al) describe various syntheses of sulfoalkyl-substituted hydroxylamines. In the preferred synthesis, a mono-substituted hydroxylamine hydrochloride or sulfate is reacted with a vinylsulfonate. Unwanted by-products are allegedly suppressed, but the desired product must be isolated using salt precipitation or ion exchange resins. The reaction is carried out in the presence of a neutralizing base which produces unwanted salts that must be removed by filtration.
It would be desirable to have a simple method for preparing substituted hydroxylamines that need not be isolated prior to use, but can be immediately used in photographic processing solutions. Thus, it is also desired to suppress the formation of significant amounts of unwanted by-products.